In the United States and many other areas of the world, grass covers millions of homesteads, private and public lawns, and mowed areas. Cutting this grass is an activity that figures in local economies and air quality worldwide. In the US alone, $30 billion is spent annually on lawn care, more than any other crop, and turf grass is estimated to cover 50 million acres (202,000 square km), twice the land area of Pennsylvania, about half of it being residential (US News & World Report 28 Oct. 1996). Among the 100 million households in the USA, many are landowners who regularly cut the grass around their homes and ranches, and over 9 million lawn mowers are sold annually in the USA. Most of these machines are powered by small internal combustion (IC) engines under 5 HP (3.7 kW) that are relatively unsophisticated and are a significant source of volatile organic hydrocarbons (VOCs), carbon monoxide (CO), and particulate emissions. Deemed a significant contributor to air pollution nationwide, the US Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) have issued new rules to restrict exhaust emissions for four stroke internal combustion engines that are typically used to power lawn and garden mowers.
Grass presents unique problems for the cutting arts. Most turf grasses found on lawns in the US are descended from tough grasses that have evolved to grow on prairies or savannahs in other parts of the world. Unlike most cutting done in the industrial arts, mowing grass is a complex process and involves a number factors. The materials to be cut are biological, unpredictable, arrayed at different angles, differing in moisture content, and mechanical characteristics from grass blade to grass blade. Plant characteristics vary from plant to plant in a single lawn or field, and from region to region. Differing individual characteristics for blades of grass include different elastic moduli, mass densities and thicknesses. This affects the specific failure modes for a grass blade under a cutting stress, and not all types of grass or conditions will allow for the same cutting behavior. Grass products tend to be wet internally, full of sticky substances such as glues and other proteins. The substrate for the grass to be cut can influence cutting efficiency and blade life and can vary from loamy or sandy soils to claylike or muddy conditions. Material buildup on cutting surfaces and associated components is a well known problem, and mower operator behavior can be unpredictable. The cutting process must occur satisfactorily the first time, on the first mower pass, and with a high degree of quality. Further, in many cases, there is a significant amount of cut material, often moist or wet, to be disposed of on the cutting field or into a receptable or bag.
Three different machines are typically used to cut turf grass lawns and similar applications: reel-type mowers, rotary mowers, and sickle mowers.
In reel mowers, grass is cut by scissors-like shearing action of a series of curved spiral-wound blades mounted on a reel. The spiral wound blades orbit a common axis, and act against a fixed straight blade or bed knife extending parallel to the common axis. The shearing action of reel mowers results in a clean cut and a smooth, green lawn surface with less tear damage to individual blades of grass. But reel mowers have many disadvantages: they cannot cut all types of grasses or weeds or light brush and they often need adjustment and sharpening. Relatively heavy, they are hard to maneuver and cannot cut grass close to walls or trees. They have cumbersome and expensive drive trains, owing to the relatively slow rotational speed of the reel and the horizontal orientation of its rotation axis. Reel mowers also cannot cut many types of plant stalks, including dandelion seed stalks, and are generally only used for short mowing heights, e.g., under 1 inch (2.54 cm) Ref: Guidelines for Professional Turf and Groundcover Management, Jay Deputy, Landscape L-11, CTAHR, University of Hawaii at Manoa Cooperative Extension Service, October 2000, pp. 1-6. They are more costly and require more maintenance and operator knowledge for successful mowing. Reel mowers constitute perhaps 3% of all lawn mowers in the US, and are mostly used by professional turfgrass maintenance personnel where a large capital expenditure for purchase, and increased maintenance is more readily tolerated. Furthermore, the shearing action used by reel mowers comes at the expense of high running friction between the spiral blades of the reel and the straight stationary blade that it contacts, due to the strong clamping force (inter-blade bias) needed to maintain successful shearing action, much as one endeavors to keep each blade of a pair of scissors tightly applied against one another to get a good cut. With component wear, some adjustments are typically needed to maintain true shearing action.
Reel mowers are also extremely limited in their ability to handle upsets from obstructions and non-negotiable plant stalks, resulting in frequent jamming. For this reason, a high reserve torque is needed to drive the reel, and in spite of that, operator intervention is still often needed when mowing rough lawns, meadows or light brush.
Rotary mowers cut grass by the action of a rapidly turning or orbiting pitched sharp blade at the end of a vertical driven shaft or disc. Tangential velocity of these sharp blades can reach 27 m/s or 60 miles/hour, and a high tangential speed is required for a successful cut. Rotary mowers are the market volume leaders in lawn cutting equipment, and are advantageous in that they can be used in grass or weeds or light brush of almost any height, and they are relatively inexpensive. However, they are inherently dangerous and represent a domestic hazard of the highest order for operators, producing thousands of injuries each year, many of a serious nature. Rotary mowers will cut through most objects which come into contact with its rotating blade, and will throw hard objects such as rocks, stones or other debris that come into the path of the blade rotation. Manufacturers have used housings or skirts surrounding the rotary blade path, but the skirt must be shallow at the forward end so as to be open to incoming grass without bending the grass excessively, and must include a discharge chute or via. Often the discharge chute and the nearby housing become clogged with grass clippings, rendering the mower useless. This tempts operators to either tilt the mower to expose the underside for cleaning or inspection, or to actually attempt to clean the affected area while the mower is running, both inviting severe and immediate danger. Many operators are injured by deliberate or accidental placement of a foot under this housing, wherein the foot, or merely a shoe lace or pant cuff projects sufficiently so as to be caught by the moving blade. This can happen when pushing or negotiating the mower over uneven ground, and particularly on wet hillsides. The rotating blade is a major structural element and possesses in a dangerous way substantial rotational inertia, due to its own radial extent and weight, and also due to the rotational inertia of any blade support disc used, and that of the crankshaft, piston(s) and valvetrain of any internal combustion engine used or that of the heavy motor armature of any electric motor used. If the rotary mower is used inappropriately, such as has been done by some to lift it in the air to trim hedges and the like, it can maim and kill in seconds.
Furthermore, rotary mowers are basically crude and destructive chopping devices which rely on impact cutting or tearing of the grass rather than shearing it cleanly, causing plant damage which in turn causes vulnerability to disease, moisture loss and pests, and causes the lawn to have a brown cast after mowing. Rotary mowers require blade sharpening, and emit loud noise, mostly due to the high IC engine output required and due to windage losses, as the pitched blade is customarily designed to be used to create a strong updraft to insure grass blades are straightened and vertical for subsequent cutting. The tensile failure cut given by a rotary mower requires more energy, and the high torque capacity prime movers needed for most mowers generally, are wasteful, as discussed below. Very little of the applied power in either type of mower goes toward grass cutting itself, and the rotating blades used need periodic sharpening.
Sickle mowers are used successfully in many farming applications such as to harvest tall grains like wheat, and beans, and operate in a way analogous to a barber's electric clippers, by employing, in various possible arrangements, rows of teeth that slide by each other or move relative to one another. This provides an effective cutting action without moving a fixed blade through open space as with the rotary mower. In this sense, the term sickle mower could be interpreted by some as a misnomer.
Various sickle mower arrangements and cutting techniques are disclosed in the prior art, among them, US Patent Application Publication No. US 2002/0035827 A1 and U.S. Pat. No. 6,305,154 to Yang et al.; and also U.S. Pat. No. 6,314,707 to Ryan; U.S. Pat. No. 6,076.265 to Huang Lo; U.S. Pat. No. 6,062,012 to Suarez et al.; U.S. Pat. Nos. 5,875,624 and 5,644,904 to Olinger; U.S. Pat. Nos. 5,845,474 and 5,732,539 to Loftus; U.S. Pat. Nos. 5,706,639 and 5,557,913 to Metz; U.S. Pat. Nos. 5,398,490 and 5,261,217 to Allen; U.S. Pat. No. 5,372,001 to Olson et al.; U.S. Pat. No. 5,201,168 to Jenson; U.S. Pat. No. 5,123,237 to Lutz; U.S. Pat. No. 4,866,921 to Nagashima et al.; U.S. Pat. No. 4,651,511 to Majkrzak; U.S. Pat. No. 4,198,803 to Quick et al.; U.S. Pat. No. 4,048,791 to Treen; U.S. Pat. No. 4,044,534 to Day et al.; U.S. Pat. No. 3,978,645 to Bennett et al.; U.S. Pat. No. 3,973,378 to Bartasevich et al.; U.S. Pat. No. 3,934,340 to Jones et al.; U.S. Pat. No. 3,756,000 to Kerr; U.S. Pat. No. 3,664,103 to McNair; U.S. Pat. No. 3,657,868 to Cousino; U.S. Pat. No. 3,656,285 to Carlson; U.S. Pat. No. 3,641,752 to Ipbach; U.S. Pat. No. 3,633,346 to Thomas J. McMullen; U.S. Pat. No. 3,397,524 to W. D. Hofer; U.S. Pat. No. 3,242,659 to O. L. Dunlap; U.S. Pat. No. 3,006,129 to V. A. Sayre; U.S. Pat. No. 3,006,126 to A. D. VIVERETTE; U.S. Pat. No. 2,793,487 to T. H. WOBERMIN; U.S. Pat. No. 2,714,280 to S. D. Baker; U.S. Pat. No. 2,186,126 to W. H. Roll; U.S. Pat. No. 2,079,945 to W. H. Manning; U.S. Pat. No. 1,775,421 to R. O. Clark; U.S. Pat. No. 1,647,867 to E. O. Hutsell; U.S. Pat. No. 1,258,671 to G. O. Greenfield; U.S. Pat. No. 845,547 to R. W. Hathaway; U.S. Pat. No. 765,126 to O. R. Chaplin; and U.S. Pat. No. 153,755 to E. W. Crawford et al; all of which are hereby incorporated herein in their entirety.
The cutting action of a sickle mower is safer, since the sickle blades move transversely against one another, and safety can be afforded by making the spaces between teeth relatively small to as to generally allow only grass and small brush to be entrained therein. Sickle mowers tend to use less input energy per cut than reel or rotary mowers, because little or no energy is expended for actions such as circumferentially and upwardly moving grass, re-cutting grass, and moving air; and in the case of a rotary mower, there is no exhaust throw of grass and secondary cutting products out a chute or via (see FIGS. 1 and 2 below).
However, prior art sickle mowers have important limitations. Sickle mowers almost always use multiple blades, e.g., 20 blades, and it is usually essential to maintain sickle blade sharpness for proper operation, because there is less reliance or little reliance on impact cutting, as is done in rotary mowers. Sharpening of the multiple sickle blades is relatively difficult, and usually requires specific component re-assembly beyond the capability of most consumers. Blade lifetimes are often limited and sickle bars containing the blades are often heavy and cumbersome. Also, one often cannot obtain effective cutting for sickle mowers cutting grass, as some grass encountered on the cutting field tends to flatten or simply move in a way so as to avoid being trapped in the sickle mechanism. Sickle mowers are usually therefore often used on larger types of vegetation such as found in fields, orchards and ditches.
Grass capture considerations are vital to the success of any sickle mower. U.S. Pat. No. 3,656,285 to Carlson reviews problems of the prior art and concludes that the efficiency of a sickle mower using a toothed band or sickle blade set depends greatly on the individual characteristics of the grass blades being cut. Blades of grass that need a small amount of trimming, such as encountered when mowing a lawn regularly, are not always cut, as some blades of grass are not stiff enough to allow mechanical resistance to motion that would cause them to enter the active sickle cutter; instead, selected grass blades are pushed aside or knocked aside as the mower passes, without being cut. The solution, as seen by Carlson and others, is to bring the grass into the cutting device, and to keep it there during the cutting action, much as a barber pulls or combs hair into the path of his scissors. In the reel mower, the moving spiral blades accomplish this function; in the rotary mower, the updraft created by the rotating pitched blade(s) maintains the grass blades in a relative vertical position for cutting by blade impact. Carlson accomplishes this for a sickle mower by using an endless mowing band that comprises grass gathering clasps to urge individual grass blades into bunches to be cut, rather than bending out of the cutters's influence. Carlson's embodiments also include fixed and moving elements to keep the cutting apparatus clean and free from accumulated grass that would otherwise be thrown out the discharge chute in a rotary mower.
In the typical prior art sickle mower, there is a moving cutting blade set that moves laterally against either [1] another moving cutting blade set moving in the opposite direction; or [2] one or two or three stationary blade sets, which in this disclosure shall be called stators (see Definitions below). Between the planes established by the moving cutting blades and the stator(s) there is a dimensional or spatial gap, which tends to be large, and therefore not conducive for cutting fine grass. The large gap, discussed below, means that the actual failure mode tends to be a either: [1] tensile failure in the grass, which requires more energy to accomplish, and tends to cause grass damage as cited above; or if the sickle blade is kept sharp, [2] a knife cut, similar to an impact cut, with some grass body cleavage from the sharpness of the sickle cutting blade. For example, U.S. Pat. No. 5,845,474 to Loftus teaches use of blades that are knives, arrayable into a blade set or blade chain.
One of the important objects of this invention is to provide for a successful sickle mower for consumer use in cutting turf grass which consumes little energy and could be run with a very small IC engine or, preferably, with a small electric motor/battery set. In the sickle mower, there are challenges and considerations relating to load management and dealing with obstructions, such as thick brush, debris, sticks, or soft stalks. Up to now, single, dual and triple stator sickle cutters have operated at high reserve torque, with a prime mover (IC engine or, in theory, an electric motor) that is geared or run so as to be able to handle sharp increases in load torque during obstructions or heavy loads, without stalling. This allowed for uninterrupted operation, but the energy required basically consigned sickle mowers to use of the same size and type of relatively large and wasteful prime mover (typically a 3-5 HP IC engine) as used by reel and rotary mowers, with much of the same high energy use, high noise levels, high exhaust emissions, and high weight and complexity associated with these traditional machines. See Ref: Busey, P., and Parker, J. H. 1992. Energy conservation and efficient turfgrass maintenance, in: Waddington, D. V., Carrow, R. N., and Shearman, R. C. (eds.) Turfgrass, pp. 473-500. American Society of Agronomy, Madison, Wis.; also Ref: Fluck, R. C., and Busey, P. 1988, Energy for mowing turfgrass, Transactions of the ASAE, American Society of Agricultural Engineers 31:1304-1308.
The high reserve torque needed by prior art sickle mowers not only results in energy wasted for running the machine, but also the high transient forces developed by necessity to plow through, cut through, or otherwise eliminate obstructions as best as possible means that the cutting blades themselves, and possibly the stator(s) digits or elements as well, have to be thick and of heavy construction to withstand shocks and to able to plow into obstructions without dings or damage. This further increases the requirement for sharp blades, as they tend to be thick, and if presented to the grass on the cutting field in dull geometry, the mower stalls, fails to cut, or cuts in an impact cut regime only, which limits its effectiveness and increases required blade lateral (cutting) velocity, further increasing the energy needed to run the mower.
Also, prior art sickle mowers, operating at high reserve torque to, in effect, have the cutting blades slam their way through grass and brush, are not adapted or capable of managing non-negotiable obstructions without operator intervention, such as when the operator stops the mower and manually clears the obstruction, etc. Also, the high reserve torque applied to the sickle cutting blades virtually assures that some safety issues remain, such as the danger of severing a finger accidentally interposed between the sickle cutting blade and stator(s). Furthermore, prior art sickle mowers using a single stator tend to rely on a the outcome of a single physical failure site on a blade of grass, that is, the cut must occur on at or near the particular pinch point or line created by the cutter(s). Those with dual stators that surround the moving blade as bread does a sandwich are in reality relying on a combination of an impact cut or knife cut from fast moving cutting blades (e.g., endless cutter, single blade movement direction), and/or a tensile failure cut, such as from reciprocating blades, as the grass or brush is caught between the moving blade and the stator. The reliance on a single shear failure site changes unfavorably the cutting action kinetics, making unsuccessful cutting events more likely.
Other problems with prior art sickle mowers include: [1] the buildup of secondary cutting products or debris on cutting blades, which tends to eventually impede facile operation. Prior art teachings such as U.S. Pat. Nos. 5,557,913 and 5,706,639 to Metz disclose “C-shaped, channel-like” cutting blades or equivalent cutting elements, but none teach how to reduce troublesome buildup of secondary cutting products (grass bits, resins, etc.) from accumulating on those blades; [2] lingering problems of conditioning the grass to not bend or move out of the way of the moving cutter blades; [3] energy wasted by the necessity of having high blade numerical redundancy, whereby energy is wasted by having a large number of blade passes in cutting zones for a given amount of forward motion of the mower, to mask or compensate for unsuccessful cutting events. As a result, no commercially successful low energy sickle mower system for consumer use in caring for turfgrass has been heretofore devised.
It is therefore one objective of this invention to provide for the creation of a low energy sickle mower and system for consumer use that does not require high reserve torque or high power capacity prime movers, and which is operator-safe, efficient, quiet, lightweight and easy to maneuver;
It is another objective of this invention to provide a sickle mower system utilizing a low energy non-interference true shear process using a dull blade for low maintenance requirements;
It is another objective of this invention to provide embodiments giving rip-free true shearing of grass using a dull thin blade moving between two stators or by one stator to improve lawn quality and reduce required energy for cutting, whereby shear cutting occurs at an upper or at a lower leading edge of cutting blade moving laterally across the cutting field in relation to mower forward motion, providing two possible twin possible shear failure sites for grass to be cut, improving cutting action kinetics and the probability of successful cutting events;
It is another objective of the invention to reduce energy wasted by the necessity of having high blade numerical redundancy, whereby energy is saved by using a minimum number of blade passes for a given amount of mower forward motion;
It is yet another objective of this invention to improve blade cleanliness and aid proper sickle operation by introducing clean-blade geometries and processes;
It is yet another objective of this invention to improve cutting action kinetics relative to prior art sickle mowers by orienting the mower for best possible results and conditioning the grass for the best possible probability of cutting success, reducing the probability that grass will move or bend out of the influence of the sickle cutter(s);
It is yet another objective of this invention to allow for load leveling or load phase shifting to reduce further needed applied power and torque;
It is still further another objective of this invention to use the benefits of the non-interference shear process to allow for torque management and blade clearing, including motor torque monitoring and clearing the cutting blade(s) of obstructions, secondary cutting products, and debris by [1] freeing and rejecting, or [2] kicking out obstructions, without requiring high energy and high reserve torque to be applied thereto, and without power surges or blade damage.
Many other important objectives and differences from the prior art will become apparent upon reading the remainder of the specification and the appended claims.